Gas leakage monitoring method and its system

ABSTRACT

A gas leakage monitoring method and system capable of ensuring safety of a gas utilization facility by visualizing invisible-to-naked-eye leakage gas and/or flame of leakage gas into the form of an image. The gas leakage monitoring method comprises the steps of collecting a detected light of a particular wavelength, which is caused by leakage gas and/or a flame of the leakage gas, in a space to be monitored, converting the detected light into an electronic image, amplifying and then converting the electronic image into an optical image again, and imaging the spatial intensity distribution of the particular wavelength light. The gas leakage monitoring system comprises first means for collecting a detected light of a particular wavelength, which is caused by leakage gas and/or a flame of the leakage gas, in a space to be monitored, second means for converting the detected light into an electronic image, and amplifying and then converting the electronic image into an optical image again, and third means for imaging the spatial intensity distribution of the particular wavelength light.

TECHNICAL FIELD

The present invention relates to a technique for visualizinginvisible-to-naked-eye gas and/or flame into the form of an image,thereby, for example, remotely determining the presence or absence of agas leakage and/or a flame, a leakage point, and a high-temperaturedangerous region with high safety. More particularly, the presentinvention relates to a gas leakage monitoring method and system, whichare adapted for continuous monitoring and are suitably used for, e.g.,the operation of a hydrogen gas utilization facility, such as hydrogensupply stations and fuel cells, and monitoring of a hydrogen gasleakage.

BACKGROUND ART

Hitherto, leakage gas has been detected by bringing sucked gas intodirect contact with a sensor portion and measuring gas concentrationbased on a change in value of electrical resistance or current. However,such a known gas detector is of the sensor type that an area capable ofbeing monitored by one detector is narrow and leakage gas cannot bedetected unless the gas reaches the detector. Accordingly, there hasbeen a risk that, in the event of a gas leakage, an alarm error mayoccur depending on the direction of wind and the position where thedetector is installed. Another problem is that, in a gas refinery or thelike, a very large number of gas detectors must be installed and asubstantial cost is required (see Patent Reference 1).

On the other hand, to solve the above-mentioned problem, a gasvisualizing device for remotely monitoring the presence of a gas leakagehas been proposed. Such a gas visualizing device employs a laser beamsource for irradiating an infrared laser beam having the same wavelengthas the absorption wavelength of gas to be measured, and the absorptionof an infrared ray, which is reflected from the background, is imagedusing an image sensor to be displayed in the form of a two-dimensionalvisible image.

However, that known gas visualizing device requires a very large-sizedand high-power laser beam source and therefore has a serious problem inpoint of cost. Another problem is that the displayed two-dimensionalimage is greatly affected by weather conditions and temperatures, and adifficulty arises in discriminating the occurrence of a gas leakage fromshinning of sunlight. For those reasons, the known gas visualizingdevice has not been suitable for monitoring a gas leakage in practicalfields (see Patent Reference 2).

Further, in the case of hydrogen gas, in spite of being an energy mediumwith a high risk in such a point as causing explosion if ignited, thehydrogen gas is tasteless, colorless, and odorless. In addition, even ifignited, a flame of hydrogen gas is substantially transparent andinvisible to the naked eye under sunlight. Meanwhile, severalpublications disclose detection techniques of selecting ultravioletlight generated upon the occurrence of corona discharge by aninterference filter, collecting an ultraviolet ray having passed throughthe interference filter, and visualizing the collected ultraviolet rayin the form of a visible image using an ultraviolet image tube or a TVcamera (see Patent References 3 and 4).

Patent Reference 1 Japanese Patent Laid-open No. 6-307967 PatentReference 2 Japanese Patent Laid-open No. 6-288858 Patent Reference 3Japanese Patent Publication No. 5-40874 Patent Reference 4 JapaneseUtility Model Laid-open No. 61-174680

DISCLOSURE OF THE INVENTION

In environments utilizing and storing gases, it has been usual that agas leakage is monitored by installing a stationary gas detector in aplace where the gas tends to reside, while locating the leakage pointhas been performed by personnel carrying a portable gas detector andgoing round of inspection. In particular, hydrogen gas is very difficultto locate the leakage point for the reasons that the hydrogen gas istasteless, colorless, and odorless and the known city gas detector orthe like cannot be used, as it is, to detect the hydrogen gas because ofdifferent properties of those gases. Accordingly, there has beendemanded a monitoring technique capable of detecting a gas leakage andlocating the leakage point in a continuous manner.

Also, a device for detecting ultraviolet rays generated from flames andissuing an alarm has been put into practical use. However, when a flameis invisible to the naked eye under sunlight in the daytime (e.g., inthe case of a hydrogen flame), it has been difficult to take an optimumaction because of incapability in safely locating the ignition pointeven with such a device being operated. In addition, that device coversa wide range of wavelength of ultraviolet rays as a detection target andtherefore may detect even an ultraviolet ray (e.g., sunlight reflectedby a window glass) other than those generated from flames in some cases.This leads to a problem that the device is susceptible to malfunctionand reliability is insufficient.

Further, because a region where hot air generated by a flame is ejectedand reside, or actual temperatures around wall surfaces, pipes, etc.,which are heated to high temperatures, cannot be sensed with the nakedeye, a difficulty arises in confirming a high-temperature region aroundthe flame, thus making it harder to stop the leakage gas and performextinguishing activities.

When observing a flame by a thermo-camera for visualizing an infraredray, radiation from high-temperature portions, such as wall surfaces andpipes heated by the flame, is so strong that it is difficult to locatethe flame shape and the position where the flame is generated.

In addition, a device for detecting an infrared ray generated from aflame and issuing an alarm has been further put into practice, but sucha device has also not yet succeeded in overcoming the difficulty inconfirming a high-temperature region around the flame.

An object of the present invention is to solve the problems set forthabove.

More specifically, an object of the present invention is to provide agas leakage monitoring method and system, which can realize thefollowing demands:

-   -   1. Visualization of leakage gas    -   2. Visualization of a flame    -   3. Visualization of a high-temperature dangerous region

With the view of realizing those demands, the present invention isintended, on the basis of the Raman scattering phenomenon that when alaser beam is irradiated to gas or a liquid, the wavelength of the laserbeam is shifted by an amount of energy corresponding to the absorptionenergy of a molecule, to detect a gas leakage by imaging the spatialintensity distribution of the Raman scattering light and to locate aleakage point by superimposing a distribution image over a backgroundimage.

Also, the present invention is intended, upon the occurrence of a flame,to detect an ultraviolet ray generated from the flame, to detect theoccurrence of the flame by amplifying and imaging a weak light of aparticular wavelength, and to locate a frame generation point and/or ahigh-temperature dangerous region by superimposing a background imageand/or a flame image and/or an infrared ray image with each other.

According to one aspect of the present invention, there is provided agas leakage monitoring method comprising the steps of collecting, in atarget space to be monitored, a detection target light of a particularwavelength generated from leakage gas and/or a flame of the leakage gas,converting the collected light into an electronic image, amplifying theelectronic image, and converting the amplified electronic image into anoptical image again, thereby imaging a spatial intensity distribution ofthe particular wavelength light.

According to another aspect of the present invention, the detectiontarget light generated from the leakage gas is a Raman scattering lightgenerated from measurement target gas with irradiation of a laser beamto the target space to be monitored.

According to still another aspect of the present, the detection targetlight of the particular wavelength is collected by an optical band-passfilter having a transmission wavelength center in match with thewavelength of a spectrum line of the Raman scattering light generatedfrom the measurement target gas.

According to still another aspect of the present invention, thedetection target light of the particular wavelength is collected onlyfor a certain time calculated based on a return time of the laser beamor the Raman scattering light.

According to still another aspect of the present invention, a gasleakage point is located by superimposing a background image of thetarget space to be monitored and the imaged spatial intensitydistribution of the Raman scattering light with each other.

According to still another aspect of the present invention, a distanceto the gas leakage point is calculated based on a return time of thelaser beam or the Raman scattering light.

According to still another aspect of the present invention, thedetection target light generated from a fire of the leakage gas is anultraviolet light.

According to still another aspect of the present invention the detectiontarget light of the particular wavelength is collected by an opticalband-pass filter having a transmission wavelength center in match withthe wavelength of an emission spectrum line of an OH-group.

According to still another aspect of the present invention, the gasleakage monitoring method further comprises the steps of collecting aninfrared light of a particular wavelength in the target space to bemonitored, converting the collected light into an electronic image,amplifying the electronic image, and converting the amplified electronicimage into an optical image again, thereby imaging a spatial intensitydistribution of the infrared light in the target space to be monitored;and superimposing the imaged spatial intensity distribution of theinfrared light and the imaged spatial intensity distribution of theparticular wavelength light with each other, thereby locating a flamegeneration point of the leakage gas.

According to still another aspect of the present invention, the gasleakage monitoring method further comprises the steps of collecting aninfrared light of a particular wavelength in the target space to bemonitored, converting the collected light into an electronic image,amplifying the electronic image, and converting the amplified electronicimage into an optical image again, thereby imaging a spatial intensitydistribution of the infrared light in the target space to be monitored;and superimposing the imaged spatial intensity distribution of theinfrared light and the background image of the target space to bemonitored with each other, thereby locating a high-temperature dangerousregion.

According to still another aspect of the present invention, in the stepof collecting the infrared light of the particular wavelength in thetarget space to be monitored, a transmission light is selected by anoptical band-pass filter allowing an infrared spectrum of 7 μm to 14 μmto pass through the filter.

According to still another aspect of the present invention, there isprovided a gas leakage monitoring system comprising first means forcollecting, in a target space to be monitored, a detection target lightof a particular wavelength generated from leakage gas and/or a flame ofthe leakage gas; second means for converting the collected detectiontarget light into an electronic image, amplifying the electronic image,and converting the amplified electronic image into an optical imageagain; and third means for imaging a spatial intensity distribution ofthe particular wavelength light.

According to still another aspect of the present invention, the gasleakage monitoring system further comprises means for irradiating alaser beam to the target space to be monitored, wherein the first meanscomprises a condenser lens and an optical band-pass filter having atransmission wavelength center in match with the wavelength of aspectrum line of the Raman scattering light generated from themeasurement target gas; the second means comprises an image intensifier,an image pickup device, and a signal processing unit; and the thirdmeans is a program for imaging a detected signal.

According to still another aspect of the present invention, the gasleakage monitoring system further comprises synchronizing signaltransmission means for synchronizing the laser beam irradiation meansand the second means with each other, the synchronizing signaltransmission means operating the second means only for a certain timecalculated based on a return time of the laser beam or the Ramanscattering light.

According to still another aspect of the present invention, the firstmeans and the laser beam irradiation means are disposed in coaxialrelation.

According to still another aspect of the present invention, the gasleakage monitoring system further comprises means for picking up abackground image of the target space to be monitored; and means forsuperimposing the spatial intensity distribution of the particularwavelength light imaged by the third means and the background imagepicked up by the background image pickup means with each other, therebylocating a gas leakage point.

According to still another aspect of the present invention, the gasleakage monitoring system further comprises means for calculating adistance to the gas leakage point based on a return time of the laserbeam or the Raman scattering light.

According to still another aspect of the present invention, the firstmeans comprises a condenser lens and an optical band-pass filter havinga transmission wavelength center in match with the wavelength of anemission spectrum line of an OH-group; the second means comprises animage intensifier, an image pickup device, and a signal processing unit;and the third means is a program for imaging a detected signal.

According to still another aspect of the present invention, the firstmeans comprises a condenser lens, a first optical band-pass filterhaving a transmission wavelength center in match with the wavelength ofa spectrum line of the Raman scattering light generated from themeasurement target gas, and a second optical band-pass filter having atransmission wavelength center in match with the wavelength of anemission spectrum line of an OH-group; the second means comprises animage intensifier, an image pickup device, and a signal processing unit;and the third means is a program for imaging a detected signal, thefirst means being capable of using the first optical band-pass filterand the second optical band-pass filter in a switchable manner.

According to still another aspect of the present invention, the gasleakage monitoring system further comprises means for picking up abackground image of the target space to be monitored; and means forsuperimposing the spatial intensity distribution of the particularwavelength light imaged by the third means and the background imagepicked up by the background image pickup means with each other, therebylocating a flame generation point of the leakage gas.

According to still another aspect of the present invention, the gasleakage monitoring system further comprises infrared image pickup meansfor collecting an infrared light of a particular wavelength in thetarget space to be monitored, converting the collected light into anelectronic image, amplifying the electronic image, and converting theamplified electronic image into an optical image again; and means forsuperimposing the background image picked up by the background imagepickup means and the infrared image picked up by the infrared imagepickup means, thereby locating a high-temperature dangerous region.

According to still another aspect of the present invention, the infraredimage pickup means comprises a condenser lens, an optical band-passfilter allowing an infrared spectrum of 7 μm to 14 μm to pass throughthe filter, and a thermo-camera.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a gas leakage monitoring method according tothe present invention.

FIG. 2 is a flowchart showing an outline of a leakage gas detectingprocess according to the present invention.

FIG. 3 is a flowchart of a process for locating a gas leakage pointaccording to the present invention.

FIG. 4 is a flowchart showing an outline of a flame visualizing processaccording to the present invention.

FIG. 5 is a flowchart of a process for locating a flame generation pointaccording to the present invention.

FIG. 6 is a flowchart of a process for locating a high-temperaturedangerous region according to the present invention.

FIG. 7 is a block diagram showing the configuration of a gas leakagemonitoring system according to the present invention.

FIG. 8 a is a time chart showing a Raman scattering light capturing(monitoring distance of 1.5 m-8 m).

FIG. 8 b is a time chart showing a Raman scattering light capturing(monitoring distance of 3 m-6 m).

FIG. 9 is a block diagram showing the configuration of a gas leakagemonitoring system according to Embodiment 1.

FIG. 10 is a block diagram showing the configuration of a lightreceiving optical system according to Embodiment 1.

FIG. 11 is a graph showing an emission spectrum of a hydrogen flame.

FIG. 12 a is a flowchart (1/4) of the processing executed in the gasleakage monitoring system according to Embodiment 1.

FIG. 12 b is a flowchart (2/4) of the processing executed in the gasleakage monitoring system according to Embodiment 1.

FIG. 12 c is a flowchart (3/4) of the processing executed in the gasleakage monitoring system according to Embodiment 1.

FIG. 12 d is a flowchart (4/4) of the processing executed in the gasleakage monitoring system according to Embodiment 1.

FIG. 13 is a schematic diagram showing an experimental system accordingto Embodiment 2 in which hydrogen is used as target gas.

FIG. 14 is a graph showing the spectrum of a Raman scattering lightemitted from hydrogen according to Embodiment 2.

FIG. 15 is a graph showing the relationship between the hydrogenconcentration and the intensity of the Raman scattering light accordingto Embodiment 2.

FIG. 16 is a schematic diagram showing the configuration of anexperimental system for verifying visualization of leakage gas accordingto Embodiment 3.

FIG. 17 shows the relationship between the hydrogen concentration andcolored images according to Embodiment 3.

FIG. 18 shows a visualized image of a flame according to Embodiment 3.

FIG. 19 is a block diagram of a gas leakage monitoring system accordingto Embodiment 4.

FIG. 20 is a block diagram of a gas leakage monitoring system accordingto Embodiment 5.

FIG. 21 is a block diagram of a laser-scanned leakage gas visualizingsystem according to Embodiment 6.

FIG. 22 is a block diagram of a gas leakage monitoring system formeasuring a backscattered light according to Embodiment 7.

FIG. 23 a is a graph showing the intensity of the Raman scattering lightmeasured from the backside according to Embodiment 7.

FIG. 23 b is a graph showing the intensity of the Raman scattering lightmeasured in a lateral direction according to Embodiment 7.

REFERENCE NUMERALS

1 light receiving optical system, 2 objective lens, 3 optical band-pathfilter, 4 image intensifier, 5 eyepiece, 6 photoelectric surface, 7electronic lens, 8 micro-channel plate, 9 fluorescent surface, 10personal computer (PC), 11 CCD camera adapted for Raman scatteringlight, 12 CCD camera adapted for visible light, 13 monitoring controlprogram, 14 image processing program, 15, 16, 17 image memory, 18monitor screen, 19 speaker (alarm device), 20 LAN (communication means),21 display of gas generation position, 30 thermo-camera, 40 condenserlens, 41 laser beam scanner, 42 oscillating mirror, 43, 44 photodetector, 45 laser unit, 46 beam distributor, 47 control/processingunit, 200 laser beam transmission system, 201 laser unit, 202transmission optical system, and 203 time synchronizing signal generator

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the present invention will be describedbelow with reference to the drawings.

FIG. 1 is a flowchart showing an outline of processing executed in a gasleakage monitoring method and system according to the present invention.Steps 1 to 3 represent a process for visualizing leakage gas, and steps4 to 6 represent a process for visualizing a flame. As shown in FIG. 1,monitoring of leakage gas is continued until gas detection (steps 1 and2). If leakage gas is detected, a leakage point is located (step 3).After the gas detection, monitoring of a flame is continued until flamedetection (steps 4 and 5). If a flame is detected, a high-temperaturedangerous region is located (step 6).

While FIG. 1 is illustrated as monitoring a flame after the detection ofleakage gas, the steps 1 to 3 and the steps 4 to 6 may be performedseparately not in a time sequential order.

Procedures of the leakage gas visualizing process executed in the steps1 to 3 will be described in more detail below.

The process for detecting leakage gas is performed as shown in FIG. 2.First, an optical band-path filter is selected to set a wavelength forobserving a Raman scattering light (step 11). Because the Ramanscattering wavelength differs for each type of gas to be monitored aslisted in Table 1 given below, it is required to prepare a plurality ofoptical band-path filters having different centers of transmissionwavelengths and select suitable one from among them. Then, a pulsinglaser beam is irradiated to a space to be monitored (step 12), and alight of only a particular wavelength is extracted from Raman scatteringlights induced from the leakage gas upon irradiation of the laser beam(step 13). The extracted light is collected and converted into anelectronic image, followed by amplifying the electronic image andconverting it into an optical image again, whereby the optical image isformed (step 14). On that occasion, noises due to disturbance lights,etc. can be cut by synchronizing the timing of collecting the Ramanscattering light with the timing of irradiating the laser beam pulse tothe monitored space (step 15). Then, the intensity of the Ramanscattering light is converted into an electrical signal by an imagepickup device, and the spatial intensity distribution of the Ramanscattering light is obtained in the form of a visible image based on therecorded signal (step 16). The necessity of taking any action for theleakage gas, such as issuance of an alarm, is determined depending onwhether the spatial intensity distribution of the Raman scattering lightexceeds a threshold (step 17).

When sunlight or an object having a high photo-reflectance for otherillumination light comes into the view field of an image pickup means,the signal intensity is increased in both the wavelength range of theRaman scattering light and the other wavelength range. In such a case,the real Raman scattering light cannot be regarded as being detected andtherefore the detection of a gas leakage is not determined.

The process for locating a gas leakage point is performed as shown inFIG. 3. A background image (visible image) I_(B) of the monitored spaceis picked up by a background image pickup means such as a CCD camera(step 21), and the background image I_(B) is stored in an imageprocessing system (step 22). Then, the ultraviolet image having beenimaged in the step 16 is captured into the image processing system (step23), and is subjected to binary processing to leave only areas of theultraviolet image having values of not less than a threshold (step 24).A resulting binary-processed image is colored (step 25), and a coloredimage I_(F) is stored in the image processing system (step 26). Bysuperimposing the background image I_(B) and the colored image I_(F)with each other, the gas leakage point is visualized so that the gasleakage point can be located (step 27). The distance to the gas leakagepoint can be calculated from a return time of the laser scattering lightor the Raman scattering light, or it can also be calculated based ontriangular surveying when there are a plurality of image pickup means(step 28).

TABLE 1 Raman Raman scattering scattering Raman wavelength wavelengthscattering (nm) for laser (nm) for laser cross- Raman shift wavelengthof wavelength of sectional Molecule (cm⁻¹) 355 nm 266 nm area for N₂ CO₂1286 372.0 275.4 1.1 CO₂ 1388 373.4 276.2 1.5 O₂ 1556 375.8 277.5 1.3 CO2145 384.3 282.1 1.0 N₂ 2331 387.0 283.6 1.0 H₂S 2611 391.3 285.9 6.8CH₄ 2914 396.0 288.4 11.5 CH₄ 3020 397.6 289.2 5.0 NH₃ 3334 402.7 291.95.4 H₂O 3652 407.9 294.6 2.8 H₂ 4160 416.5 299.1 3.1

Procedures of the flame visualizing process executed in the steps 4 to 6will be described in more detail below.

The flame visualizing process according to the present invention isperformed as shown in FIG. 4. First, to select the transmissionwavelength in a light receiving system, an optical band-path filter isset so as to have the transmission wavelength center at each ofwavelengths of OH-group emission spectrum lines (i.e., for a light ofeach wavelength of 280 nm or 309 nm), and to allow passage of the lightof such each wavelength through the filter in a wavelength range ofseveral nm (step 31). When the light receiving system is used in commonwith the leakage gas visualizing method, the optical band-path filter isswitched over to an appropriate one. Then, only an ultraviolet light ofthe wavelength near 280 nm or 309 nm is extracted by the opticalband-path filter (step 32). The ultraviolet light is collected by alight collecting optical system and converted into an electronic image,followed by amplifying the electronic image and converting it into anoptical image again, whereby the optical image is formed (step 33).Then, the intensity of the ultraviolet light is converted into anelectrical signal by an image pickup device, and the spatial intensitydistribution of the ultraviolet light is obtained in the form of avisible image based on the recorded signal (step 34). The occurrence ofa flame is detected depending on whether the spatial intensitydistribution of the ultraviolet light exceeds a threshold (step 35).

The process for locating the flame generation point is performed asshown in FIG. 5. First, the ultraviolet image having been imaged in thestep 34 is captured into the image processing system (step 41), and issubjected to binary processing to leave only areas of the ultravioletimage having values of not less than a threshold (step 42). Then, aninfrared image is picked up by an infrared image pickup means such as athermo-camera (step 43), and is subjected to binary processing to leaveonly areas of the infrared image having values of not less than athreshold (step 44). A common area (overlapped area) between theultraviolet image and the infrared image both having been subjected tothe binary processing is colored (step 45), and a resulting coloredimage is stored in the image processing system (step 46). Then, bysuperimposing the colored image with the background image I_(B) storedin the step 22 (step 47), the fire generation point can be visualized.

The process for locating a high-temperature dangerous region isperformed as shown in FIG. 6. First, an infrared image is picked up byan infrared image pickup means such as a thermo-camera (step 51), and issubjected to binary processing to leave only areas of the infrared imagehaving values of not less than a threshold (step 52). Then, thebinary-processed infrared image is colored (step 53) and stored as acolored image I_(S) in the image processing system (step 54). Then, bysuperimposing the colored image I_(S) with the background image I_(B),the high-temperature dangerous region can be visualized (step 55). Thedistance to the high-temperature dangerous region can be calculatedbased on triangular surveying when there are a plurality of image pickupmeans. Incidentally, when the infrared image binary-processed in thestep 44 is employed in the step 53, the steps 51 and 52 are no longerrequired.

FIG. 7 shows the configuration of a gas leakage monitoring systemaccording to the present invention.

The gas leakage monitoring system according to the present inventioncomprises a laser beam transmission system, a Raman scattering lightreceiving system, a flame ultraviolet light receiving system, a timesynchronizing signal generator, a background image pickup means, aninfrared image pickup means, and an image processing system.

Among the above-mentioned components, those ones essential for detectingleakage gas are the “laser beam transmission system”, the “Ramanscattering light receiving system”, and the “image processing system”(the “time synchronizing signal generator” is preferably also requiredfrom the viewpoint of eliminating noises, such as disturbance lights).Essential components for detecting a flame are the “flame ultravioletlight receiving system” and the “image processing system”. To visualizea high-temperature dangerous region, the infrared image pickup means isfurther required. In the case of carrying out a part of the functions ofthe present invention, all the above-mentioned components are notnecessarily required.

The laser beam transmission system comprises a laser unit and atransmission optical system for irradiating a laser beam to the space tobe monitored. The transmission optical system may be constructed suchthat the laser beam is spread by a lens or the like for irradiation tothe monitored space, or that the laser beam is scanned by a scanner orthe like for irradiation to the monitored space.

The Raman scattering light receiving system comprises a light receivingoptical system for selecting a light of the measurement wavelength fromRaman scattering lights induced from the leakage gas upon irradiation ofthe laser beam by an optical band-path filter, and then collecting andfocusing the selected Raman scattering light, an image pickup device forpicking up an image focused by the light receiving system and convertingthe image into an electrical signal, and a signal processing unit forrecording the electrical signal.

The flame ultraviolet light receiving system extracts only anultraviolet light of the wavelength near 280 nm or 309 nm by an opticalband-path filter, collects the extracted ultraviolet light by a lightcollecting optical system, and converts the collected ultraviolet lightinto an electrical image. After amplifying the electronic image andconverting it into an optical image again, the optical image is formed.

To detect a flame by the Raman scattering light receiving system, anoptical band-path filter having the transmission wavelength center ateach of wavelengths of OH-group emission spectrum lines (i.e., for alight of each wavelength of 280 nm or 309 nm) must also be required inaddition to the optical band-pass filter for selecting the Ramanscattering light.

For that reason, in the case of detecting leakage gas and detecting afire by one light receiving system, it is required to construct thoseoptical band-pass filters in a switchable manner.

The time synchronizing signal generator is connected to both the laserunit and the light receiving optical system of the Raman scatteringlight receiving system, and generates a reference signal for holding thetiming of irradiating the laser beam to the monitored space and thetiming of starting and ending the reception of the Raman scatteringlight in synchronized relation. The timing of irradiating the laser beamand the timing of receiving the Raman scattering light differ dependingon the distance to the target gas to be monitored. For example, when thedistance to the monitoring target is in the range of about 1.5 m to 8 m,the process is performed in accordance with such a time chart (FIG. 8 a)that, because of the light velocity being about 30 cm/1 nano second,image capturing is started with a delay of 10 nano seconds after theirradiation of the laser beam and is continued for a time of 45 nanoseconds. When the distance to the monitoring target is in the range ofabout 3 m to 6 m, the process is performed in accordance with such atime chart (FIG. 8 b) that image capturing is started with a delay of 20nano seconds after the irradiation of the laser beam and is continuedfor a time of 20 nano seconds.

The background image pickup means is an image pickup means, such as aCCD camera, and picks up a background image for locating the leakage gasand/or the flame position.

The infrared image pickup means comprises a light collecting opticalsystem for collecting a thermal spectrum, and an image pickup means,such as a thermo-camera. Then, the infrared image pickup means picks upan infrared image for locating a high-temperature dangerous region.

The image processing system includes a processing program for imagingthe detected signal.

The present invention will be described below in more detail inconnection with examples of the gas leakage monitoring method and systemaccording to embodiments of the present invention. It is to be notedthat the present invention is in no way limited by the followingembodiments.

Embodiment 1

FIG. 9 shows one example the configuration of a gas leakage monitoringsystem according to Embodiment 1.

The system of Embodiment 1 is able to monitor leakage gas, locate a gasleakage point, monitor a flame, and to visualize a high-temperaturedangerous region.

Referring to FIG. 9, numeral 10 denotes a personal computer including animage processing program. Connected to the personal computer 10 are atime synchronizing signal generator 203 and a Raman scattering lightadapted camera 11 a both serving as a leakage gas image pickup means, avisible light adapted camera 12 serving as a background image pickupmeans, an ultraviolet light adapted camera 11 b serving as a flame imagepickup means, and a thermo-camera 30 serving as an infrared image pickupmeans via cables.

Image pickup targets of the Raman scattering light adapted camera 11 aand the ultraviolet light adapted camera 11 b are set to the monitoringtarget. When an optical band-pass filter 3 is constructed in aswitchable manner, the Raman scattering light adapted camera 11 a andthe ultraviolet light adapted camera 11 b can be mounted in the samehousing.

The visible light adapted camera 12 and the thermo-camera 30 are eachprovided with a wide-angle lens so as to pickup an image of thebackground with lights in a wavelength range not containing the Ramanscattering light over a wide region including the monitoring target.

Numeral 200 denotes a laser beam transmission system comprising a laserunit 201 and a transmission optical system 202. The laser beamtransmission system two-dimensionally irradiates a pulsing laser beam toan area to be monitored.

The irradiation of the laser beam can be turned on/off by controllingthe laser unit from the personal computer via a cable, or byissuing/cutting a signal outputted from the time synchronizing signalgenerator 203.

Numeral 1 denotes each light receiving optical system 1 that serves asan image pickup means according to Embodiment 1. As shown in FIG. 10,the light receiving optical system 1 comprises an objective lens 2serving as a light collecting optical system, an optical band-passfilter 3 serving as a transmission light selecting means, an imageintensifier 4 serving as an ultraviolet light amplifying/visualizingmeans, and an eyepiece 5.

The objective lens 2 comprises a condenser lens, a relay lens, and alens barrel (not shown) so that an image of the observation target canbe formed on an imaging surface of the image intensifier 4.

The image intensifier 4 comprises a photoelectric surface 6 formed of athin film disposed on the side facing the optical band-pass filter 3 andhaving the external photoelectric effect, an electronic lens 7, amicro-channel plate 8, and a fluorescent surface 9. An ultraviolet lighthaving passed through the optical band-pass filter 3 is converted intoan electronic image by the photoelectric surface 6. The electronic imageis focused by the electronic lens 7 and is subjected to secondaryelectron amplification by the micro-channel plate 8. Then, the amplifiedelectronic image is returned to an optical image again by thefluorescent surface 9. In this way, a weak Raman scattering light fromleakage gas and an ultraviolet light from a flame are converted intovisible images.

Incidentally, the optical band-pass filter 3 and the objective lens 2can be reversed in order of arrangement from the illustrated one.

The optical band-pass filter 3 of the Raman scattering light adaptedcamera 11 a has the center of transmission wavelength for observing thewavelength of the Raman scattering light from the gas to be monitored.The central wavelength for each kind of gas to be monitored is as shownin Table 1 given above.

The optical band-pass filter 3 of the ultraviolet light adapted camera11 b has the center of transmission wavelength for a light of eachwavelength 280 nm or 309 nm and also has a transmission wavelength widthwithin a half width at half maximum of 5 nm. For example, the emissionspectrum of a hydrogen flame has, as shown in FIG. 11, an emissionregion centered at the wavelength of 280 nm and an emission regioncentered at the wavelength of 309 nm. By making the emission spectrum ofa hydrogen flame transmitted through the optical band-pass filter 3,therefore, an ultraviolet light having a wavelength range of 280 nm±5 nmor a wavelength range of 309 nm±5 nm is allowed to pass through thefilter, while lights of other wavelengths are cut off.

Although this embodiment uses the optical band-pass filter 3 describedabove, it is desirable to use a filter having a narrower transmissionwavelength width from the viewpoint of lessening disturbance influences,such as sunlight and other illumination. For that reason, a band-passfilter having a transmission wavelength range with a full width at halfmaximum of 1.5 nm is preferably used. By using such a band-pass filterhaving a transmission wavelength range with a full width at half maximumof 1.5 nm, disturbance lights can be reduced and the flame can be moreclearly observed than the case of using a band-pass filter having awider transmission wavelength range. On the other hand, widening thetransmission width of the transmission wavelength range leads to anadvantage that a background image can be captured along with a flameimage and the visible light adapted camera 12 can be omitted.

A Raman scattering light is generated based on a phenomenon induced uponirradiation of a laser beam. For example, when a high-speed pulsinglaser beam is irradiated, the Raman scattering light is also generatedin the form of a high-speed pulse. By measuring the pulsing Ramanscattering light in time synchronized relation to the laser irradiation,the Raman scattering light can be discriminated from disturbances, suchas sunlight and other illumination lights which moderately vary withtime, and a sharper gas distribution image can be observed.

In the light receiving optical system of the Raman scattering lightadapted camera 11 a, a voltage applied to the electronic lens 7 of theimage intensifier 4 is controlled in sync with the irradiation pulse ofthe laser beam to turn on/off arrival of electrons to the micro-channelplate 8. The light reception is thereby allowed or inhibited so as toamplify only the light in a time zone in which the Raman scatteringlight is emitted (i.e., a time zone in which the laser beam isirradiated) by the micro-channel plate 8. With such gate-on/offoperation, it is possible to minimize influences of disturbances, suchas sunlight, other illumination lights, and laser induced fluorescencefrom the monitored area.

The visible image formed on the fluorescent surface 9 of the imageintensifier 4 of course can be picked up by the Raman scattering lightadapted camera 11 a and the ultraviolet light adapted camera 11 b, andvisually observed even by the naked eye through the eyepiece 5.

The thermo-camera 30 serving as an infrared image pickup means comprisesa light collecting optical system 30A for collecting a heat spectrum dueto black body radiation emitted from air, vapor, piping equipment, etc.around a flame, which are heated by the flame, an optical band-passfilter serving as a transmission light selecting means that allowstransmission of a light of 7 μm-14 μm through the filter to select theheat spectrum collected by the light collecting optical system 30A, andan image receiving surface on which an infrared image of the heatspectrum selected by the optical band-pass filter is formed. With thatconstruction, the thermo-camera 30 converts the infrared image of aflame into an electrical signal.

The light collecting optical system 30A comprises an objective lens, arelay lens, and a lens barrel so that an image of the observation targetcan be formed on an image receiving surface of the thermo-camera 30.

The infrared light having passed through the light collecting opticalsystem 30A and the optical band-pass filter is converted into anelectronic image by the thermo-camera 30 and then converted into avisible image. The infrared image representing an infrared lightdistribution region captured by the thermo-camera 30 can also bevisually observed by the naked eye through an eyepiece lens system.

The personal computer 10 is connected to the Raman scattering lightadapted camera 11 a, the ultraviolet light adapted camera 11 b, thevisible light adapted camera 12, and a LAN 20, and contains a monitoringcontrol program 13 for executing monitoring control. The monitoringcontrol program 13 includes an image processing program 14 forcontrolling image processing executed in the Raman scattering lightadapted camera 11 a, the ultraviolet light adapted camera 11 b, thevisible light adapted camera 12, and the thermo-camera 30.

Then, an image processing means in this Embodiment 1 is made up of thepersonal computer 10, the monitoring control program 13, the imageprocessing program 14, an input means (not shown) such as a keyboard ora mouse, and a monitor screen 18.

When gas of the measurement target is detected or when a flame isdetected, the monitoring control program 13 issues an alarm through aspeaker 19 or informs the detected fact to the other component, e.g.,the personal computer via the LAN 20. Also, when gas of the measurementtarget is detected or when a flame is detected, the monitoring controlprogram 13 gives warnings of the place under monitoring or the positionof an apparatus monitored and the occurrence of an abnormality in theform of characters and voices.

The image processing program 14 is able to display the images picked upby the Raman scattering light adapted camera 11 a and the ultravioletlight adapted camera 11 b, the background image picked up by the visiblelight adapted camera 12, and the infrared image picked up by thethermo-camera 30 on one monitor screen 18 at the same time in anydesired combination. Also, the background image picked up by the visiblelight adapted camera 12, the infrared image picked up by thethermo-camera 30, and the images picked up by the Raman scattering lightadapted camera 11 a and the ultraviolet light adapted camera 11 b can bedisplayed in superimposed relation to each other in any desiredcombination.

By way of example, the image picked up by the Raman scattering lightadapted camera 11 a can be displayed in superimposed relation to thevisible image picked up by the visible light adapted camera 12 throughthe steps of combining the visible image picked up by the visible lightadapted camera 12 and the image picked up by the Raman scattering lightadapted camera 11 a with each other, which are outputted respectively toimage memories 15, 16 in a video board of the personal computer 10,storing a composite image in an image memory 17, and outputting thecomposite image to the monitor screen 18 so that both the images can berecognized at the same time.

Next, a flow of processing executed in the gas leakage monitoring systemof this Embodiment 1 is shown in FIGS. 12 a through 12 d.

As shown in the flowchart of FIG. 12 a, when monitoring control isstarted (START), the background image (visible image) is first picked upby the visible light adapted camera 12 (step 61). The picked-upbackground image is stored as a visible image (I_(B)) in accordance withthe image processing program 14 (step 62). Then, an ultraviolet image ofa target area for detection of leakage gas is picked up by the Ramanscattering light adapted camera 11 a (step 63). The ultraviolet imagepicked up by the Raman scattering light adapted camera 11 a is subjectedto binary processing in accordance with the image processing program 14(step 64). In this binary processing, the ultraviolet image is comparedwith a preset threshold, and a value of not less than the threshold isdetermined as indicating the target gas. The image processing program 14calculates an area of the binary-processed image (i.e., the Ramanscattering intensity) (step 65).

The image processing program 14 compares the calculated Raman scatteringintensity (i.e., the Raman spectrum intensity) with a prescribed valueset in advance (step 66). This prescribed value is previously set inaccordance with the monitoring control program 13 or during initialsetting of the image processing program 14, for example, in anadjustable manner.

If the Raman scattering intensity does not exceed the prescribed value,the image processing program 14 colors the binary-processed image (step67), stores a colored image I_(F) (step 68), and displays the coloredimage I_(F) and the background image I_(B) on the screen 18 insuperimposed relation (step 69). A display time of the composite imagecan be set at any desired interval, e.g., 10 seconds or 1 minute, whichis optionally adjustable in accordance with the monitoring controlprogram 13 or the image processing program 14. Then, after the lapse ofa predetermined time, the control flow returns to a point upstream ofthe step 61 for the continued monitoring of the target area.

If the Raman scattering intensity exceeds the prescribed value, theimage processing program 14 determines that the target gas is leaked,followed by executing the processing shown in FIG. 12 b. Morespecifically, the image processing program 14 transmits commands to themonitoring control program 13 so as to make such emergent actions asissuing an alarm through the speaker 19, stopping the supply of gas,and/or sprinkling water to suppress a temperature rise caused uponfiring (step 71). Additionally, the gas leakage monitoring system may beconstructed by installing an alarm unit and communication equipment suchthat, when the ultraviolet ray of the Raman scattering light from thetarget gas is detected on the photoelectric surface 6 or when an imageof the target gas is imaged on the fluorescent surface 9, an alarm isautomatically issued in response to a detected signal of such an image.

Subsequently, the image processing program 14 colors thebinary-processed image (step 72), stores a colored image I_(F) (step73), and displays the colored image I_(F) and the background image I_(B)on the screen 18 in superimposed relation, thereby visualizing theleakage gas (step 74). The distance to the leakage gas is calculatedbased a time lapsed from the irradiation of the laser beam to arrival ofthe Raman scattering light, thereby locating the leakage point (step75).

If there occurs gas leakage, the occurrence of a flame is monitored insuccession. As shown in a flowchart of FIG. 12 c, when monitoring of aflame is started, an ultraviolet image of the target area for gasleakage detection is first picked up by the ultraviolet light adaptedcamera 11 b (step 81). The picked-up ultraviolet image of a flame issubjected to binary processing in accordance with the image processingprogram 14 (step 82). Subsequently, an infrared image is picked up bythe infrared light image pick-up means, such as the thermo-camera (step83), and is subjected to binary processing in accordance with the imageprocessing program 14 (step 84). Then, the image processing program 14calculates an area of a common portion (overlapped portion) between theultraviolet image and the infrared image each having beenbinary-processed image (step 85).

If the area of the common portion does not exceed the prescribed value,the image processing program 14 colors the common portion (step 87),superimposes the colored image I_(h) and the background image I_(B) witheach other (step 88), and displays both the images on the screen 18(step 89). A display time of the composite image can be set at anydesired interval of, e.g., 10 seconds or 1 minute, which is optionallyadjustable in accordance with the monitoring control program 13 or theimage processing program 14. Then, after the lapse of a predeterminedtime, the control flow returns to a point upstream of the step 81 forthe continued monitoring of the target area.

If the area of the common portion exceeds the prescribed value, theimage processing program 14 determines that there has occurred a flame,followed by executing the processing shown in FIG. 12 d. Morespecifically, the image processing program 14 transmits commands to themonitoring control program 13 so as to make such emergent actions asissuing an alarm through the speaker 19 and/or operating a sprinkler(step 91). Additionally, the gas leakage monitoring system may beconstructed by installing an alarm unit and communication equipment suchthat, when the ultraviolet image of the flame is formed on thephotoelectric surface 6 or when a flame image is formed on thefluorescent surface 9, an alarm is automatically issued in response to adetected signal of such an image. Subsequently, the image processingprogram 14 colors the binary-processed flame image (step 92), stores acolored image I_(h) (step 93), and superimposes the colored image I_(h)and the background image I_(B) with each other (step 94), therebydisplaying both the images on the screen 18. As a result, the flame isvisualized and the flame generation point is located (step 95).

Locating a high-temperature dangerous region will be described below. Asshown in a flowchart of FIG. 12 d, after locating the flame generationpoint, an infrared image of the flame detected region is picked up bythe thermo-camera 30 (step 96). The picked-up infrared image issubjected to binary processing in accordance with the image processingprogram 14 (step 97). In this binary processing, the infrared image iscompared with a preset threshold, and a pixel having a value of not lessthan the threshold is determined as indicating the high-temperaturedangerous region. The image processing program 14 colors thebinary-processed image (step 98) and stores a colored image I_(S) (step99). Then, the colored image I_(S) picked up by the thermo-camera 30 andthe background image I_(B) are superimposed with each other anddisplayed on the screen 18 (step 100). A display time of the compositeimage can be set at any desired interval, e.g., 10 seconds or 1 minute,which is optionally adjustable in accordance with the monitoring controlprogram 13 or the image processing program 14. Then, after the lapse ofa predetermined time, the control flow returns to a point upstream ofthe step 96 for the continued monitoring of the target area until amonitoring stop command is issued.

[Effect of Embodiment 1]

With the leakage gas monitoring system, as described above, since thelight receiving optical system 1 converts the target gas into a visibleimage and the image processing program 14 displays the target gas andthe background image through combination processing, it is possible tovisually confirm a leakage of the target gas and/or the situation ingeneration of a flame and/or the high-temperature dangerous region.

Also, since the monitoring control program 13 has at least one of thefunction of issuing an alarm from the speaker 19 or a buzzer and thefunction of sending information or communicating a notice via the LAN 20when the light receiving optical system 1 has detected the target gas F,the occurrence of an emergent state can be notified at once. As a matterof course, the keyboard or the mouse (not shown) can be used to controlthe monitoring control program 13, the image processing program 14, andother programs when plural sets of the Raman scattering light adaptedcameras 11 a, the ultraviolet light adapted cameras 11 b, the visiblelight adapted cameras 12, and the thermo-cameras 30 are connected to thepersonal computer 10.

When a wide area or a plurality of places are to be monitored, themonitoring can be performed by connecting each set of the Ramanscattering light adapted camera 11 a, the ultraviolet light adaptedcamera 11 b, the visible light adapted camera 12, the thermo-camera 30and so on to a network. In this case, if the light receiving opticalsystem 1 installed in any of the places detects the target gas F, theimage processing program 14 displays the position where the target gas Fhas been generated, i.e., the position of the occurrence of a leakage ofthe target gas and/or the flame on the monitor screen 18 (positiondisplay means), in accordance with a signal identifying the lightreceiving optical system 1 that has detected the target gas F.

Such display 21 of the occurrence of a leakage of the target gas and/orthe generation position of a flame displays the background image andblinking large-sized preset characters on the monitor screen 18. It istherefore possible to certainly recognize the target leakage point andto take operations for stopping supply of the target gas and preventingthe spread of a fire.

Further, the monitoring control program 13 can record the position ofeach light receiving optical system 1, characters and voices as specificinformation in advance, and can display the leakage point on the screenor announcing it with voices through local area broadcasting inaccordance with ID information (information for identifying each lightreceiving optical system 1) transmitted from the light receiving opticalsystem 1 when a leakage of the target gas is detected.

In addition, when the light receiving optical system 1 has detected thetarget gas F, the monitoring control program 13 can also close a targetgas supply valve near the leakage point of the target gas F or sprinklewater from a distinguishing means, such as a fireplug, in accordancewith the identification information of the light receiving opticalsystem 1 that has detected the target gas F.

According to the gas leakage monitoring system constructed as describedabove, even when leakage gas is invisible to the naked eye, the leakagegas can be visually recognizable with the naked eye, and thereforemonitoring of colorless and transparent gas can be realized in a spaceto be monitored. By using an electronic image pickup means instead ofthe visual monitoring with the naked eye, it is possible to electricallycapture respective images of the target gas and/or the flame and/or thehigh-temperature dangerous region.

Embodiment 2

FIG. 13 is a schematic diagram showing an experimental system in whichhydrogen is used as the target gas.

An experiment was conducted by employing the system configuration shownin FIG. 13, hydrogen gas as the target gas, and a 266-nm fourth harmonicof a YAG laser as the laser beam source. As a result, as shown in FIG.14, the Raman scattering spectrum emitted from the hydrogen gas has anemission region about a wavelength 299.1 nm being as the center.Correspondingly, the optical band-pass filter 3 has the transmissionwavelength center for a light having a wavelength of 299.1 nm and itstransmission wavelength range has a half width at half maximum of 1 nm.Thus, the optical band-pass filter allows an ultraviolet light having awavelength range of 299.1 nm±1 nm to pass through the filter, and cutsoff lights of other wavelengths. When strong fluorescence is generatedin an environment for measuring the Raman scattering light, themeasurement can also be made using the Raman scattering light shiftedtoward the shorter wavelength side.

In addition, as a result of conducting an experiment by employing thesystem configuration shown in FIG. 13, hydrogen gas as the target gas,and a 266-nm fourth harmonic of a YAG laser as the laser beam source,correlation between the concentration of hydrogen gas and the spatialintensity of the Raman scattering light was confirmed as shown in FIG.15. Therefore, the concentration of leaked hydrogen gas can be measuredby detecting the spatial intensity of the Raman scattering light.

Embodiment 3

FIG. 16 is a schematic diagram showing the configuration of anexperimental system for verifying visualization of leakage gas.

As a result of conducting an experiment for verifying visualization ofleakage gas by employing the system configuration shown in FIG. 16,hydrogen gas as the target gas, and a 266-nm fourth harmonic of a YAGlaser as the laser beam source, an image of the Raman scattering lightwas obtained as shown in FIG. 17.

The optical band-pass filter has a central wavelength of 299.1 nm, andits transmission wavelength range has a half width at half maximum of 1nm.

FIG. 17 shows the colored images at various values of the hydrogenconcentration. As shown in FIG. 17, the colored image becomes clearer bydegrees as the hydrogen concentration increases.

FIG. 18 shows a visualized image of a hydrogen flame, which is obtainedby coloring the image measured using the above-described system.

The optical band-pass filter has a central wavelength of 308.8 nm, andits transmission wavelength range has a half width at half maximum of1.5 nm. While an exposure gate time was set to 80 μs for picking up animage in the measurement of this embodiment, a gate can be kept open.

Embodiment 4

FIG. 19 shows another embodiment of the gas leakage monitoring systemaccording to the present invention.

In the embodiment of FIG. 19, a half mirror allowing an ultravioletlight to pass through the mirror is used to introduce the Ramanscattering light from the target gas to the Raman scattering lightadapted camera for picking up an image of the leakage gas, while thebackground image is introduced to the visible light adapted camera sothat optical axes of both the cameras are aligned with each other.

Embodiment 5

FIG. 20 shows still another embodiment of the gas leakage monitoringsystem according to the present invention.

In the embodiment of FIG. 20, the laser beam and the Raman scatteringlight are introduced through respective optical fiber cables. Therefore,this embodiment is suitable for detecting leakage gas in, e.g., a deadspace of a structure or a closed conduit. The laser beam is irradiatedthrough one optical fiber, and the Raman scattering light and thebackground light are focused at an end face of another optical fiberthrough a focusing lens. Then, a half mirror allowing an ultravioletlight to pass through the mirror is used to introduce the Ramanscattering light from the target gas to the Raman scattering lightadapted camera for picking up an image of the leakage gas, while thebackground image is introduced to the visible light adapted camera sothat optical axes of both the cameras are aligned with each other.

Embodiment 6

FIG. 21 shows the configuration of an embodiment of a laser-scanned gasleakage monitoring system according to the present invention.

The laser-scanned gas leakage monitoring system according to thisembodiment comprises a laser transmission system made up of a laser unit45, a beam distributor 46, a photo-detector 44 and a laser beam scanner41 comprising two oscillating mirror 42, a light receiving system madeup of a condenser lens 40 and a photo-detector 43, andcontrol/-processing unit 47 including a control mechanism for thescanner 41 to control the irradiation position of the laser beam, alsoincluding a time synchronizing mechanism for controlling the timing ofreceiving the Raman scattering light with respect to the laserirradiation, and two-dimensionally imaging the position of the laserirradiation and the distribution of the Raman scattering light.

A part of a pulsing laser beam emitted from the laser unit 45 is changedin its direction by the beam distributor 46 so as to enter thephoto-detector 44. A quartz plate and a photodiode are used respectivelyas the beam distributor 46 and the photo-detector 44.

An optical band-pass filter (not shown) having a center wavelengthmatched with the Raman wavelength of the target gas is disposed in frontof a light receiving device of the photo-detector 43, and the condenserlens 40 for increasing the amount of received light is further disposedin front of the photo-detector 43. The photo-detector 43 is constitutedby a photomultiplier tube or an APD (Avalanche photodiode).

By arranging another set of the photo-detector 43 along with an opticalband-pass filter having a center wavelength matched with the wavelengthof the laser beam and the condenser lens 40, it is possible to capturesituations of the surroundings other than the target gas undermonitoring in a three-dimensional way, and to confirm a spread ofleakage gas from combination with the distance information obtainedbased on a Raman signal.

The leakage gas is detected by irradiating the laser beam emitted fromthe laser unit 45 to be scanned in a θ-direction (corresponding to avertical tilt angle: Y axis) and in a φ-direction (corresponding to ahorizontal angle: X axis) by the laser scanner 41, and receiving theRaman scattering light from the leakage gas by the photo-detector 43.

Based on the irradiation position of the laser beam and the signal fromthe photo-detector 43, data regarding a position (Xn, Yn) of the targetgas under monitoring and data regarding the intensity of the Ramansignal are calculated to sequentially display changes in the intensityof the Raman signal at a position (xn, yn) on the display, whichcorresponds to the target area. Alternatively, by recording the data ofthe position data and the intensity of the Raman signal in match withscanning of the laser beam, an image may be formed after scanning theentirety of the target area.

The distance from the monitoring system to the target gas is calculatedfrom the information measured by the photo-detector 44. Morespecifically, a part of the laser beam emitted from the laser unit 45 istaken out by the beam distributor 46 and detected by the photo-detector44. A time until receiving the signal from the photo-detector 43 ismeasured with a signal from the photo-detector 44 being a reference (0second). The measured time interval represents a time required for thelaser beam to reach the target gas and for the Raman scattering light toreturn from the target gas to the monitoring system. As a result, thedistance from the monitoring system to the target gas can be calculatedfrom the measured time interval.

Embodiment 7

The Raman scattering light from the target gas is scattered in largeramount in a direction exactly opposed to the direction in which thelaser beam is irradiated (namely, a large part of the Raman scatteringlight is backscattered). Therefore, when the Raman scattering light ismeasured in a direction perpendicular to the irradiation direction ofthe laser beam (i.e., in a lateral direction) as in Embodiment 3 (i.e.,in the case of the system configuration shown in FIG. 16), it maysometimes happen that the Raman scattering light is too weak to measure.In this embodiment, to avoid such a trouble, the Raman scattering lightis measured from the backside by a gas leakage monitoring systemconfigured to receive the backscattered light, as shown in FIG. 22.

A holed mirror is used to measure the Raman scattering light that isgenerated in a direction (backward) coaxial with the laser beam when thelaser beam is irradiated to the measuring cell. The irradiated laserbeam passes through a hole in the holed mirror, while the Raman lightbackscattered from the measuring cell is reflected by a mirror portionof the holed mirror to enter the lens, followed by being collected ontoa slit of a spectrometer. On that occasion, because the collected lightincludes a component corresponding to the laser beam reflected by awindow plate of the measuring cell, an attenuation filter for the laserbeam (266 nm) is used to attenuate the laser beam component (266 nm).

As a result of irradiating nitrogen gas (N₂), water vapor (H₂O), andhydrogen gas (H₂) with the system configuration shown in FIG. 22, aspectrum of the Raman scattering light was obtained as shown in FIG. 23a. On the other hand, as a result of measuring a spectrum of the Ramanscattering light with the system configuration of FIG. 16 according toEmbodiment 3, the spectrum was obtained as shown in FIG. 23 b. Asunderstood from those results, the system configuration for measuringthe Raman scattering light from the backside is able to capture theRaman scattering light at larger intensity, and therefore it is morepreferable as the configuration of the leakage gas detecting system.

INDUSTRIAL APPLICABILITY

According to the gas leakage monitoring method and system of the presentinvention, since an ultraviolet image of the Raman scattering lightgenerated from target gas is selected by the optical band-pass filter ofthe image pickup means and the ultraviolet image is picked up throughthe image intensifier, it is possible to recognize the target gas evenwhen it is colorless, transparent and invisible to the naked eye.

Also, the image of the target gas captured by the image pickup means canbe converted into a visible image by the image processing means anddisplayed on the monitor, for example.

Further, the Raman scattering light generated from only the target gascan be selected by using the optical band-pass filter having a narrowband.

Moreover, by receiving the Raman scattering light generated from thetarget gas corresponding to the irradiated laser beam, a leakage of thetarget gas can be detected with certainty. Depending on the wavelengthof the irradiated laser beam, a gas image can also be captured as animage of the scattered visible light.

In addition, since situations around a leakage point of the target gascan also be displayed as a background image on the monitor screen, it ispossible to confirm the leakage point of the target gas in a short timeand to promptly take actions such as stopping supply of the target gas.

According to the gas leakage monitoring method and system of the presentinvention, since an ultraviolet image of a flame is selected by theoptical band-pass filter of the image pickup means and the ultravioletimage is picked up through the image intensifier, it is possible torecognize the flame even when it is invisible to the naked eye.

Also, the image of the flame captured by the image pickup means can beconverted into a visible image by the image processing means anddisplayed on the monitor, for example.

Further, since situations around a position where a flame occurs, gascan also be displayed as a background image on the monitor screen, theflame generation position can be confirmed in a short time.

Moreover, by capturing an infrared image with the infrared image pickupmeans, a high-temperature dangerous region can be recognized in an areawhere there is another heat source, such as hot air or a leakage ofcurrent.

In addition, by displaying the flame image, the background image, andthe infrared image in superimposed relation, it is possible to confirmthe flame generation position and the high-temperature dangerous region,and therefore to smoothly take further actions for distinguishing afire.

1. A gas leakage monitoring method, comprising steps of: collecting alight at a wavelength in a target space to be monitored, therebyobtaining a collected light; converting the collected light into anelectronic image; amplifying and converting the electronic image into anoptical image and imaging a spatial intensity distribution of the lightat the particular wavelength light; and superimposing the obtained imageon a background image of the target space to be monitored and displayingleakage gas on the background image of the target space to be monitored.2. The gas leakage monitoring method according to claim 1, furthercomprising a step of irradiating a laser beam to a target space to bemonitored before the step of collecting a light, wherein the step ofcollecting a light includes collecting a Raman scattering light at awavelength that is Raman-shifted by a predetermined value from thewavelength of the irradiated laser beam depending on a kind of targetgas to be monitored, and wherein said spatial intensity distribution ofthe light is a spatial intensity distribution of the Raman scatteringlight.
 3. The gas leakage monitoring method according to claim 2,wherein the Raman scattering light of the particular wavelength iscollected only for a certain time calculated based on a return time ofthe laser beam or the Raman scattering light.
 4. The gas leakagemonitoring method according to claim 3, wherein the leakage gas isdisplayed in different colors depending on concentrations of the leakagegas in the target space to be monitored.
 5. The gas leakage monitoringmethod according to claim 3, wherein the target gas to be monitored isselected from gases listed in Table 1 given below, and saidpredetermined values of the Raman shift are numerical values listed inTable 1 TABLE 1 Raman shift (cm⁻¹) CO₂ 1286 or 1388 O₂ 1556 CO 2145 N₂2331 H₂S 2611 CH₄ 2914 or 3020 NH₃ 3334 H₂O 3652 H₂ 
 4160.


6. The gas leakage monitoring method according to claim 1, wherein thestep of collecting a light includes collecting, in a target space to bemonitored, an ultraviolet light at a wavelength of about 309 nm whichcorresponds to an emission spectrum line of an OH-group, wherein thespatial intensity distribution of the light is a spatial intensitydistribution of the ultraviolet light at the particular wavelength, andwherein the step of superimposing includes displaying a flame caused byhydrogen gas on the background image of the target space to bemonitored.
 7. The gas leakage monitoring method according to claim 6,the method further comprising the steps of collecting, in the targetspace to be monitored, an infrared spectrum of 7 μm to 14 μm,superimposing an infrared light image at the particular wavelengthobtained through the imaging process and the ultraviolet light image atthe particular wavelength obtained through the imaging process with eachother, to thereby extract a common portion between the infrared andultraviolet light images, and superimposing the extracted image on thebackground image of the target space to be monitored, thereby displayinga flame caused by hydrogen gas on the background image of the targetspace to be monitored.
 8. The gas leakage monitoring method according toclaim 7, the method further comprising the step of superimposing theinfrared light image at the particular wavelength obtained through theimaging process and the background image of the target space to bemonitored with each other, thereby displaying a high-temperaturedangerous region on the background image of the target space to bemonitored.
 9. A gas leakage monitoring system comprising: a lightreceiver including a condenser lens, an optical band-pass filter havinga transmission wavelength center at a wavelength of a light spectrumfrom leakage gas, an image intensifier, an image pickup device, and asignal processing unit, wherein said light receiver collecting a lightat a particular wavelength depending on a kind of gas to be monitored ina target space, converting the collected light into an electronic image,amplifying the electronic image and converting the amplified electronicimage into an optical image and obtaining imaged spatial intensitydistribution of the light at the particular wavelength; a visual imagepickup for capturing an image of visible light in the target space to bemonitored; an image processor for imaging a spatial intensitydistribution of the light at the particular wavelength based on a signalfrom said light receiver, said image processor superimposing the imageof visible light obtained by said visual image pickup and the imagedspatial intensity distribution of the light at the particular wavelengthwith each other and displaying leakage gas on the visible light image ofthe target space to be monitored.
 10. The gas leakage monitoring systemaccording to claim 9 further comprising: a laser beam irradiator toirradiate laser beam to a target space to be monitored, wherein saidoptical band-pass filter has a transmission wavelength center at thewavelength of a Raman scattering light spectrum from leakage gas,wherein said light receiver collects a light at a wavelength that isRaman-shifted by a predetermined value from the wavelength of theirradiated laser beam depending on the kinds of target gas to bemonitored, converts the collected light into an electronic image,amplifies the electronic image, and converts the amplified electronicimage into an optical image again and obtains imaged spatial intensitydistribution of the Raman scattering light at the particular wavelength,and wherein said image processor images a spatial intensity distributionof the Raman scattering light at the particular wavelength based on asignal from said light receiver, superimposes the image of visible lightobtained by said visual image pickup device and the imaged spatialintensity distribution of the Raman scattering light at the particularwavelength with each other, and displays leakage gas on the visiblelight image of the target space to be monitored.
 11. The gas leakagemonitoring system according to claim 10, further comprisingsynchronizing signal transmission means for transmitting a synchronizingsignal for operating said light receiving means to collect the lightonly for a certain time calculated based on a return time of the laserbeam or the Raman scattering light.
 12. The gas leakage monitoringsystem according to claim 11, wherein said light receiver and said laserbeam irradiation means are disposed in coaxial relation.
 13. The gasleakage monitoring system according to claim 11, wherein said imageprocessor displays the leakage gas in different colors depending onconcentrations of the leakage gas in the target space to be monitored.14. The gas leakage monitoring system according to claim 10, wherein thegas to be monitored is selected from gases listed in Table 2 givenbelow, and said predetermined values of the Raman shift are numericalvalues listed in Table 2 TABLE 2 Raman shift (cm⁻¹) CO₂ 1286 or 1388 O₂1556 CO 2145 N₂ 2331 H₂S 2611 CH₄ 2914 or 3020 NH₃ 3334 H₂O 3652 H₂
 4160.


15. The gas leakage monitoring system according to claim 10, whereinsaid light receiver further includes an optical band-pass filter havinga transmission wavelength center at about 309 nm which corresponds to anemission spectrum line of an OH-group, and changes over said opticalband-pass filter having the transmission wavelength center at thewavelength of the Raman scattering light spectrum from leakage gas andsaid optical band-pass filter having a transmission wavelength center atabout 309 nm such that an ultraviolet light at a particular wavelengthcaused by a flame of hydrogen gas can be collected, and said imageprocessor produces an image of a spatial intensity distribution of theultraviolet light at the particular wavelength based on a signal fromsaid light receiver, and superimposing the obtained image on the visiblelight image of the target space to be monitored, thereby displaying theflame caused by hydrogen gas on the visible light image of the targetspace to be monitored.
 16. The gas leakage monitoring system accordingto claim 9, wherein the light receiver is an ultraviolet light receiverand the optical band-pass filter has a transmission wavelength center ofabout 309 nm which corresponds to an emission spectrum line of anOH-group, wherein said ultraviolet light receiver collects anultraviolet light at a particular wavelength which is caused by a flameof leakage gas in the target space to be monitored, converts thecollected ultraviolet light into an electronic image, amplifies theelectronic image, and converts the amplified electronic image into anoptical image again and obtains imaged spatial intensity distribution ofthe ultraviolet light at the particular wavelength, wherein said imageprocessor images the spatial intensity distribution of the ultravioletlight at the particular wavelength based on a signal from saidultraviolet light receiver, and wherein the image processor superimposesthe visible light image obtained by said visual image pickup device andthe imaged spatial intensity distribution of the ultraviolet light atthe particular wavelength with each other and displays a flame caused byhydrogen gas on the visible light image of the target space to bemonitored.
 17. The gas leakage monitoring system according to claim 16,further comprising infrared light receiver for capturing an image of aninfrared spectrum of 7 μm to 14 μm in the target space to be monitored,said image processing means superimposing the infrared light imageobtained by said infrared image pickup means and the imaged spatialintensity distribution of the ultraviolet light at the particularwavelength with each other, to thereby extract a common portion betweenthe infrared and ultraviolet light images, and superimposing theextracted image on the visible light image obtained by said visual imagepickup device, thereby displaying a flame caused by hydrogen gas on thevisible light image of the target space to be monitored.
 18. The gasleakage monitoring system according to claim 17, wherein said imageprocessor superimposes the infrared light image obtained by saidinfrared light receiver and the visible light image obtained by saidvisual image pickup device with each other, thereby displaying ahigh-temperature dangerous region on the visible light image of thetarget space to be monitored.